Last night, I left my computer running overnight with two tabs open in Firefox. When I came back in the morning, the computer had a black screen that said "Disk Boot Failure - Insert System Disk and press Enter. I know it wasn't a power outage because my sons computer was on all night as well. I rebooted the computer after I saw this message and the PC booted into Windows XP just as it normally would. I ran Firefox and it told me it would restore the two tabs that had been left open before the crash.
Could somebody please help me determine what happened here, and if there is anything wrong with my computer, hard disk drive, or other hardware?